This invention relates to a process for the preparation of stable, aqueous synthetic copolymer latexes and to the aqueous copolymer latexes produced thereby.
Aqueous dispersions of polymers, which are referred to in the art as latexes, are generally known to be useful, both alone and in various formulations, as coatings, adhesives, impregnants and the like. A wide variety of latexes of differing homopolymeric and copolymeric composition (such as styrene-butadiene copolymers, acrylic homopolymers and copolymers, vinylidene chloride homopolymers and copolymers, etc.) have been developed having specific chemical and/or mechanical properties for particular end use applications. Unfortunately, however, in the custom designing of latexes having such specialized combinations of properties, the full range of flexibility which might be thought possible in theory (e.g., on the basis of the wide variety of known, desirable characteristics individually possessed by the numerous known classes and species of addition polymerizable monomeric ingredients) have proven not to be entirely attainable in practice by virtue of complicating factors such as incompatibility as between the individual classes and/or species of the known monomeric materials; wide divergency of reactivity (or polymerization rates) as between such monomeric materials and the like. (See, for example, U.S. Pat. No. 4,002,801 at Col. 1, lines 38-64.)
In recognition of the foregoing difficulties, attempts have been made in the prior art to overcome, or to at least minimize, such difficulties. For example, in the aforementioned U.S. Patent 4,002,801, it is noted that, while certain desirable reactive monomers are not readily copolymerizable with vinyl halide and vinylidene halide monomers, such reactive monomers can nevertheless be satisfactorily introduced into vinyl halide or vinylidene halide polymers by encapsulating or "overpolymerizing" the desired vinyl or vinylidene halide homopolymer or copolymer with a copolymer (e.g., an acrylate or nitrile copolymer) with which the desired reactive monomers are compatible. Unfortunately, even that suggested improved method is not without its disadvantages and/or limitations (e.g., in terms of the types of encapsulating polymers practicable therein, the upper limit of polymer solids that can be thereby prepared without latex flocculation or coagulation, etc.). Accordingly, it would be highly desirable to provide an improved process by which two or more normally incompatible monomeric materials could be conveniently and economically emulsion polymerized to thereby form synthetic aqueous copolymer latexes having particularly desirable (and conveniently controllable) combinations of properties. In addition, it would be especially desirable to provide such an improved process which would further be widely applicable to a broad range of otherwise incompatible monomer combinations.